Rhodium (Rh)
Rhodium: The Rare and Catalytic Metal
Rhodium is a hard, shiny, silvery metal and is the rarest of all non-radioactive metals. Its name comes from the Greek word rhodon, meaning “rose,” because many of its compounds have a striking rose-red color. Today, rhodium is most famous for its role in cleaning up car exhaust.
Why Is Rhodium Useful?
Rhodium’s value comes from its incredible catalytic properties and its resistance to heat and corrosion.
Catalytic Converters: About 80% of all rhodium is used in catalytic converters for cars, where it removes harmful nitrogen oxides (NOₓ) from exhaust, turning them into harmless nitrogen and oxygen.
Chemical Industry: Rhodium acts as a catalyst in producing chemicals like nitric acid and acetic acid.
Electronics & Optics: Because it has low electrical resistance and doesn’t corrode easily, rhodium is used in electrical contacts, as a coating on optical fibers and mirrors, and even in headlight reflectors.
Other Uses: Rhodium is also used in crucibles (containers for very high temperatures) and thermocouple elements for measuring heat.
Natural Abundance & History
Rhodium is extremely rare. It can sometimes be found in river sands in pure form but is mostly recovered as a by-product of copper and nickel refining. Only about 30 tonnes are produced worldwide each year.
Discovery (1803): English chemist William Wollaston discovered rhodium while analyzing platinum ore. He noticed a brilliant red solution and extracted a new metal from it, naming it after the rose-red color of its salts.
Biological Role
Rhodium has no biological role. Some of its compounds are considered potentially carcinogenic, so it is handled with caution.